Conventional Pulse Width Modulated (PWM) inverters create common mode voltage with high frequency and dv/dt. Common-mode voltage causes motor shaft voltage, bearing current and electromagnetic interference (EMI) in the induction motor drive system. In this paper, a common-mode voltage eliminated 2-level space vector pulse width modulation scheme based on a cascaded 3-level inverter is presented. When the inverter is controlled by PWM, the common-mode voltage dropped between the neutral point of the motor and the negative terminal of the inverter supply is of alternating nature. In the proposed scheme, inverter voltage vectors having the same common mode voltage are used to generate the PWM signal. This eliminates alternating common-mode voltage and its adverse effects. The scheme is experimentally verified using a 3-level inverter realized by connecting two 2-level inverters in cascade configuration and experimental results are presented to validate the scheme.
This work proposes a Space Vector Pulse Width Modulation based scheme to eliminate the inherent problem of zero sequence voltage in an even level inverter. The scheme is presented for a 4-level inverter. Here, zero sequence voltage eliminated 4-level inversion is attained by switching amongst space vector combinations of a 7-level inverter having no zero-sequence voltage. The resulting space phasor diagram is generated, by realizing an intermediate space phasor diagram followed by translation of its vectors to switching states having no zero-sequence voltage, by simple mathematical algorithm. The scheme employs an open-end winding induction motor fed by cascaded three-level inverters from either side thereby, realizing a 7-level inverter configuration. All computations in this scheme are carried out in 60° co-ordinate system.
Common-mode voltage (CMV) generated by pulse width modulated (PWM) inverters is the root cause for the premature bearing failures and electromagnetic interference in motor drives. This CMV can be eliminated by switching zero CMV states only. This paper proposes a carrier based method for the elimination of CMV for a 3-level inverter using open-end winding (OEW) configuration for induction motor. Switching sequences and timing signals for this method are derived from the two virtual PWM patterns. In this scheme only active switching states are used to control inverter. The proposed method is free from neutral point fluctuations and clamping diodes in comparison with CMV elimination methods for conventional 3-level inverter topologies.
In recent years solid dielectrics are more commonly used as insulation for electrical equipment, as these solid dielectric elements have the properties to withstand high electric field. The properties of solid dielectric elements shall be further improved by reinforcing nano particles. This work investigates the enhancement of critical parameters of solid dielectrics using nano particles for the optimized function of power transformer. Nano solid dielectric materials are composed of epoxy resin and nano particles such as alumina (Al 2 O 3 ). The nano particles are added at different volume fractions of 0.5% and 1% with epoxy resin. The electrical and mechanical characteristics of the solid nano dielectric materials impregnated in insulating mineral oil and without mineral oil are investigated. The critical parameters such as breakdown strength, resistivity and tensile strength are measured. The tests are conducted in accordance with IS and ASTM standards.
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